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Abstract:

A time delay integration (TDI) sensor (22) comprises a sequence of cells
(42, 44, 42, 44) numbered 1 to N. The TDI sensor is configured for
transferring a charge from the cell numbered 1 via the cells numbered 2
to N-1 to the cell numbered N. Each cell (42; 44) in the sequence of
cells is either sensitive or insensitive in the sense that when the TDI
sensor (22) is evenly illuminated by light (46) incident on any of the
insensitive cells (44) is at most 90% of the intensity of the light (46)
incident on any of the sensitive cells (42). The sequence of cells (42,
44, 42, 44) comprises, in this order: a first sensitive cell (42), at
least one insensitive cell (44), and a second sensitive cell (42). An
imaging system comprising a TDI sensor and a method of imaging an object
are also disclosed.

Claims:

1. A time delay integration (TDI) sensor (22) comprising a sequence of
cells (42, 44, 42, 44) numbered 1 to N, the TDI sensor (22) being
configured for transferring a charge from the cell numbered 1 via the
cells numbered 2 to N-1 to the cell numbered N, wherein each cell (42;
44) in the sequence of cells is either sensitive or insensitive in the
sense that when the TDI sensor (22) is evenly illuminated by light (46)
having a first spectrum, the intensity of the light (46) incident on any
of the insensitive cells (44) is at most 90% of the intensity of the
light (46) incident on any of the sensitive cells (42), and wherein the
sequence of cells (42, 44, 42, 44) comprises, in this order: a first
sensitive cell (42), at least one insensitive cell (44), and a second
sensitive cell (42).

2. The TDI sensor (22) as set forth in claim 1, having associated with it
a natural number K greater than one, such that for any i, i=1 to N-K, the
cells are related as follows: if the cell numbered i is sensitive, the
cell numbered i+K is also sensitive, and if the cell numbered i is
insensitive, the cell numbered i+K is also insensitive.

3. The TDI sensor (22) as set forth in claim 1, wherein the intensity of
the light (46) incident on any of the insensitive cells (44) is zero.

4. The TDI sensor (22) as set forth in claim 1, wherein the TDI sensor is
configured for transferring the charge at discrete instants in time.

5. The TDI sensor (22) as set forth in claim 1, comprising a plurality of
cells (22) arranged in rows (28) and columns (34), each column comprising
a sequence of cells.

6. The TDI sensor (22) as set forth in claim 1, wherein the sensitive
cells (42) are arranged in a plane.

7. The TDI sensor (22) as set forth in claim 1, comprising an opaque
element (40) which is opaque at least for light (46) having the first
spectrum, the opaque element masking at least one of the insensitive
cells (44) but none of the sensitive cells (42).

8. The TDI sensor (22) as set forth in claim 1, comprising an optical
element (48) for focusing light (46) having the first spectrum on at
least one of the sensitive cells (42) but on none of the insensitive
cells (44).

9. The TDI sensor (22) as set forth in claim 8, wherein the optical
element comprises a cylindrical lens (48) or an array of lenses, for
focusing the light (46) on at least two sensitive cells (42, 42).

10. The TDI sensor (22) as set forth in claim 1, wherein the sequence of
cells (42, 44, 42, 44) is a first sequence and the TDI sensor (22)
comprises a second sequence of cells numbered 1 to N, the TDI sensor
being configured for transferring a charge from the cell numbered 1 via
the cells numbered 2 to N-1 to the cell numbered N, wherein each cell in
the second sequence of cells is either sensitive or insensitive in the
sense that when the TDI sensor (22) is evenly illuminated by light having
a second spectrum, the intensity of the light incident on any of the
insensitive cells in the second sequence is at most 90% of the intensity
of the light incident on any of the sensitive cells in the second
sequence, wherein the second sequence of cells comprises, in this order:
a first sensitive cell, at least one insensitive cell, and a second
sensitive cell, and wherein the cells in the first sequence (42, 44) are
not responsive to light having the second spectrum while the cells in the
second sequence are not responsive to light (46) having the first
spectrum.

11. An imaging system (10) for imaging an object (12), comprising a TDI
sensor (22) as set forth in claim 1; an optical system for illuminating
the object (12) and for guiding light (16; 18) from the object onto the
TDI sensor, the optical system having at least a first mode and a second
mode; a controller for synchronizing the TDI sensor (22) and the optical
system such that the TDI sensor shifts the charge from an insensitive
cell to a sensitive cell when the optical system assumes the first mode
and from a sensitive cell to an insensitive cell when the optical system
passes from the first mode to another mode.

12. The imaging system (10) as set forth in claim 11, wherein the optical
system comprises a first light source for emitting light having a third
spectrum, and a second light source for emitting light having a fourth
spectrum differing from the third spectrum.

13. The imaging system (10) as set forth in claim 1, wherein the TDI
sensor (22) is a first TDI sensor and the imaging system comprises a
second TDI sensor, the first TDI sensor (22) and the second TDI sensor
differing in their spectral response.

14. A method of imaging an object (12), comprising moving the object
relative to a TDI sensor (12) as set forth in claim 1; wherein the method
further comprises the successive steps of illuminating the object and
guiding light (16) from the object onto the TDI sensor, using a first
mode; transferring an accumulated charge to an insensitive cell (44);
illuminating the object and guiding light (16) from the object onto the
TDI sensor, using a second mode; transferring the charge to a sensitive
cell (42).

15. The method as set forth in claim 14, wherein guiding light (16) from
the object (12) onto the TDI sensor includes forming an optical image
(24) of the object on the TDI sensor and wherein the charges are moved in
accordance with the motion of the image on the TDI sensor.

Description:

FIELD OF THE INVENTION

[0001] In a first aspect, the invention relates to a time delay
integration (TDI) sensor comprising a sequence of cells numbered 1 to N,
the TDI sensor being configured for transferring a charge from the cell
numbered 1 via the cells numbered 2 to N-1 to the cell numbered N.

[0002] In a second aspect, the invention relates to an imaging system.

[0003] In a third aspect, the invention relates to an imaging method.

BACKGROUND OF THE INVENTION

[0004] In fluorescence imaging, there is often a need for detecting the
presence of multiple fluorescent labels (fluorophores) in a given sample
simultaneously. Various methods may be employed to discriminate
fluorescent labels.

[0005] In a first method, light emitted by the labels is split over
multiple detectors according to wavelength, for instance, by using
dichroic mirrors.

[0006] Another method uses the fact that different labels are usually
sensitive to different wavelengths of light for excitation. A set of
light sources, e.g. lasers, differing in their respective wavelengths, is
operated in an alternating manner. Each of the light sources typically
excites a particular set of fluorescent labels. Separate images of the
various labels can be obtained by reading out each detector before
switching to the next light source, i.e. before changing the frequency of
the illumination light. The technique is an example of time sharing or
time domain multiplexing. An advantage is that it allows using one
detector for detecting light of different frequencies. The technique thus
avoids the need for providing a separate detector for each wavelength.

[0007] The two methods can be combined so as to increase the number of
fluorophores that are detectable using a fixed number of light sources.
It is noted that the total number of fluorophores that can be detected
independently may be larger than both the number of different light
sources and the number of detectors.

[0008] In a scanning microscope with time domain multiplexing, the total
integration time per scan is increased as compared to detecting a single
type of fluorophore per sensor. However, time domain multiplexing is
still advantageous over doing multiple scans of the same area for at
least two reasons. Firstly, less time is lost to `overhead` for scanning
the sample (for, e.g., reversing the scan direction or moving the sample
back to a start position for the next scan). Secondly, changes in the
system over time have less influence on a mutual alignment of images
obtained from different excitation and/or fluorescence wavelength.

[0009] Time domain multiplexing is suitable, among others, for confocal
scanning (using, for example, non-pixelated sensors), simple line sensors
and full frame sensors. In the case of a line sensor and a continuously
moving sample, the light sources are usually switched every time the
pixel rows have been read out, so that after a single scan two or more
different full images of the same object have been acquired.

[0010] Time delay and integration (TDI) is an imaging method known to be
often faster compared to using a simple line sensor. It can be applied
both to brightfield and other imaging modalities. TDI typically uses a
special charge coupled device (CCD) having multiple adjacent rows of
pixels. As an image of the object is scanned continuously over the
sensor, the accumulated charge on the sensor is moved in a synchronous
manner from each row of pixels to the next row. Each time, only a signal
from the last row of pixels is read out and stored in memory. In this way
a signal is accumulated on the sensor with a much longer integration time
than is possible on a simple line sensor at the same scan speed.

[0011] In summary, for various applications of scanning fluorescence
imaging it is often considered advantageous to detect multiple
fluorophores on an object under study simultaneously. To this end,
multiple light sources emitting light at different wavelengths can be
employed. The light sources can be operated so as to expose the object to
light at different wavelengths in an alternating fashion. A sensor
detecting fluorescent light from the object may be read out between two
consecutive illumination periods.

[0012] FIG. 1 illustrates the principle of TDI imaging. An object 12 is
illuminated by a light source (not shown) and moved with constant speed
along an object path 14. In the Figure, only an exemplary light-emitting
point of the object 12 is graphically represented. Imaging optics 20
comprising, for example, a lens or a lens system, generates an optical
image 24 of the object 12 on a TDI sensor 22. As the object 12 moves
along the object path 12, its image 24 moves across the TDI sensor 22
along an image path 26. In the example shown, the object path 14 is a
straight line, but other paths may be envisaged, depending on the design
of the TDI sensor 22. In the example shown, the image path 26 is also a
straight line. Note that the object 12 and its image 24 move in opposite
directions, as indicated by the arrows 14, 26. The sensor 22 comprises a
plurality of parallel rows 28, each row comprising a plurality of pixels
(cells). The rows 22 comprise a first row 30 and a last row 32. While the
object 12 is located at an initial position as shown in the Figure, light
16 emitted by the object 12 is incident on the first row 30. As the
object 12 is at a final position (corresponding to the tip of the arrow
14), light 18 emitted by the object is incident on the last row 32 of the
sensor 22. Charge is accumulated on the pixels of the TDI sensor 22 as a
function of both the intensity of the optical image 24 and the time
during which the pixels are exposed to the image 24. The accumulated
charge is shifted through the sensor 22 synchronously with the movement
of the optical image 24. The signal built up by the sensor 22 is
therefore larger than that of an equivalent simple line sensor by a
factor that equals the number of pixel rows 22. During two consecutive
readouts of the TDI sensor 22 the object 12 moves over a scan length that
can be quite considerable in comparison to the size of the features of
interest of the object 12. A problem, however, is that switching between
imaging modes, such as switching of light sources, before reading out the
entire TDI sensor 22 would result in mixing of the corresponding images
on the sensor 22.

[0013] It is an object of the invention to provide a time domain
multiplexing TDI imaging method. It is another object of the invention to
provide a time domain multiplexing TDI imaging system. It is yet another
object of the invention to provide a TDI sensor for being used in a time
domain multiplexing TDI imaging system.

[0014] These objects are achieved by the features of the independent
claims. Further specifications and preferred embodiments are outlined in
the dependent claims.

SUMMARY OF THE INVENTION

[0015] According to the first aspect of the invention, each cell in the
sequence of cells is either sensitive or insensitive in the sense that
when the TDI sensor is evenly illuminated by light having a first
spectrum, the intensity of the light incident on any of the insensitive
cells is at most 90% of the intensity of the light incident on any of the
sensitive cells, and the sequence of cells comprises, in this order: a
first sensitive cell, at least one insensitive cell, and a second
sensitive cell. The charge may be transferred in consecutive steps, each
step involving a transfer of charges such that

Qafter(i+1)=Qbefore(i) (i=1 to N-1)

where Qbefore(i) is the charge in the cell numbered i before a shift
and Qafter(i) is the charge in the cell numbered i after the shift.
The cells 1 to N may be identical in construction, in which case they
differ only in their position and/or orientation. The first spectrum may
in particular be a combined spectrum of multiple light sources, in which
case the insensitive cells are "blind" to light emitted by any of the
multiple light sources. It is pointed out that the sensitive cells and
the insensitive cells may alternatively (or additionally) be
characterized by a rate at which a charge is generated in a cell when the
TDI sensor is illuminated. More precisely, each of the cells may have
associated with it a capacity for holding a charge, and when the TDI
sensor is evenly illuminated by the light having the first spectrum.
there may be a point in time at which each of the sensitive cells will
have accumulated a charge corresponding to at least 50% of its capacity
and at which each of the insensitive cells will have accumulated a charge
corresponding to at most 40% (preferably at most 20%, or at most 10%, or
at most 5%) of its capacity.

[0016] The TDI sensor may have associated with it a natural number K
larger than 1, such that for any i, i=1 to N-K, the cells are related as
follows:

[0017] if the cell numbered i is sensitive, the cell numbered i+K is also
sensitive, and

[0018] if the cell numbered i is insensitive, the cell numbered i+K is
also insensitive.

The cells are thus configured in a periodic manner. This can be
particularly convenient if the TDI sensor is to be illuminated in a
periodic manner, for instance by K alternating light sources. For
example, the sequence of cells may be designed such that the cell
numbered i (i=1 to N) is sensitive if i-1 is an integer multiple of K,
and insensitive if i-1 is not an integer multiple of K. The constant K
may, for example, be 2, 3, 4, or any other natural number.

[0019] The TDI sensor may in particular be designed such that the
intensity of the light incident on any of the insensitive cells is zero.
In such a configuration, all light is blocked from the insensitive cells.

[0020] The TDI sensor may be configured for transferring the charge at
discrete instants in time. The discrete instants may be equidistant. This
can be convenient when the TDI sensor is to be used in conjunction with
one or more periodically pulsed light sources.

[0021] The TDI sensor may comprise a plurality of cells arranged in rows
and columns, each column comprising a sequence of cells as described
above. The columns may be configured identically, in which case each of
the rows comprises either only sensitive cells or only insensitive cells.
It is pointed out, however, that the plurality cells could be arranged
very differently, for instance, along a segment of a circle, or along
segments of concentric circles. This could be convenient for scanning an
object by rotating the object relative to the TDI sensor.

[0022] The sensitive cells may be arranged in a plane. The insensitive
cells, or at least some of them, may be arranged in the same plane.
Alternatively all or at least some of the insensitive cells may be
arranged behind the plane, "behind" referring to the side of the plane
that is usually not reached be the incident light. For example, an
insensitive cell could be arranged behind a corresponding sensitive cell
such that the sensitive cell masks the insensitive cell, at least
partially, from the incident light.

[0023] The TDI sensor may comprise an opaque element which is opaque at
least for light having the first spectrum, the opaque element masking at
least one of the insensitive cells but none of the sensitive cells. The
opaque element may be reflective or absorbing, or a combination of both.
According to a preferred embodiment, the opaque element is opaque for the
entire spectrum from the far infrared to the far ultraviolet. According
to a different preferred embodiment, the opaque element is transparent
for light having higher frequencies or lower frequencies than those
contained in the first spectrum. For detecting such light, the TDI sensor
could be used as a conventional TDI sensor.

[0024] Alternatively or additionally, the TDI sensor may comprise an
optical element for focusing light having the first spectrum on at least
one of the sensitive cells but on none of the insensitive cells. More
particularly, the optical element may be configured for focusing an
incident plane wave having a frequency belonging to the first spectrum.

[0025] The optical element may comprise a cylindrical lens or an array of
lenses, for focusing the light on at least two sensitive cells. As
mentioned above, the cells may, for example, be arranged in rows and
columns, each row comprising, for example, either only sensitive cells or
only insensitive cells, cells of distinct rows belonging to distinct
sequences (i.e., charges are transferred along the columns, not along the
rows). Rows comprising only sensitive cells, and rows comprising only
insensitive cells may be referred to as sensitive rows and insensitive
rows, respectively. In this case it may be particularly convenient to
arrange a cylindrical lens in front of each sensitive row, for focusing
incident light on the respective row and for preventing at least an
important portion of the incident light from reaching insensitive rows.

[0026] The above introduced sequence of cells may be a first sequence and
the TDI sensor may comprise a second sequence of cells numbered 1 to N,
the TDI sensor being configured for transferring a charge from the cell
numbered 1 via the cells numbered 2 to N-1 to the cell numbered N,
wherein each cell in the second sequence of cells is either sensitive or
insensitive in the sense that when the TDI sensor is evenly illuminated
by light having a second spectrum, the intensity of the light incident on
any of the insensitive cells in the second sequence is at most 90%
(preferably at most 10%) of the intensity of the light incident on any of
the sensitive cells in the second sequence, wherein the second sequence
of cells comprises, in this order: a first sensitive cell, at least one
insensitive cell, and a second sensitive cell, and wherein the cells in
the first sequence are not responsive to light having the second spectrum
while the cells in the second sequence are not responsive to light having
the first spectrum. The TDI sensor may thus comprise at least two
sequences of cells of the kind discussed above, differing however in
their spectral response. Thus different spectra or different "colors"
could be detected simultaneously but independently.

[0027] The imaging system according to the second aspect of the invention
comprises [0028] a TDI sensor as described above with regard to the
first aspect of the invention; [0029] an optical system for illuminating
the object and for guiding light from the object onto the TDI sensor, the
optical system having at least a first mode and a second mode; [0030] a
controller for synchronizing the TDI sensor and the optical system such
that the TDI sensor shifts the charge from an insensitive cell to a
sensitive cell when the optical system assumes the first mode and from a
sensitive cell to an insensitive cell when the optical system passes from
the first mode to another mode. The imaging system may further comprise a
scanner for moving the object relative to the TDI sensor. The scanner may
be configured for translating the object relative to the TDI sensor along
a straight path. A speed associated with the object's motion may be
constant while the object is scanned.

[0031] The optical system may further comprise [0032] a first light
source for emitting light having a third spectrum, and [0033] a second
light source for emitting light having a fourth spectrum differing from
the third spectrum. The light having the third spectrum and the light
having the fourth spectrum may, for example, comprise different frequency
components or be differently polarized. Note that the first spectrum and
the second spectrum introduced above relate to detection characteristics
of the TDI sensor, whereas the third spectrum and the fourth spectrum
relate to the light for illuminating the object. In particular for
applications such as fluorescence imaging, where the light to be imaged
has other frequency components than the light with which the object is
illuminated, it may be advantageous to adapt the detection system to the
fluorescent light, in which case, and of course not only in this case,
the first spectrum (and/or the second spectrum) may differ from the third
spectrum (and/or the fourth spectrum). Alternatively, the third spectrum
and/or the fourth spectrum may be identical to the first spectrum or to
the second spectrum.

[0034] The TDI sensor may be a first TDI sensor and the imaging system may
comprise a second TDI sensor of the type described above, the first TDI
sensor and the second TDI sensor differing in their spectral response.
Thus different frequencies could be imaged using different TDI sensors,
in combination with time domain multiplexing of different illumination
modes.

[0035] According to the third aspect of the invention, the method of
imaging an object comprises [0036] moving the object relative to a TDI
sensor as described above with regard to the first aspect of the
invention; wherein the method further comprises the successive steps of
[0037] illuminating the object and guiding light from the object onto the
TDI sensor, using a first mode; [0038] transferring an accumulated charge
to an insensitive cell; [0039] illuminating the object and guiding light
from the object onto the TDI sensor, using a second mode; [0040]
transferring the charge to a sensitive cell.

[0041] The steps of illuminating the object and of transferring the charge
may be repeated until the charged has reached the last cell in the
sequence. After the charge has reached the last cell, the last cell may
be read out, for example, by converting the amount of the charge into a
voltage. Thus the advantages of TDI sensor-based time delay integration
methods may be combined with those of time domain multiplexing. The
technique may allow building up two different images of the object on the
sensor during a single scan.

[0042] In this context, guiding light from the object onto the TDI sensor
may include forming an optical image of the object on the TDI sensor; the
method may then include transferring the charges in accordance with the
motion of the image on the TDI sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a schematic top view of an example of a TDI imaging
system.

[0048] Unless specified otherwise, identical or similar reference numerals
appearing in different Figures refer to identical or similar components.

[0049]FIG. 2 schematically represents a front view of a TDI sensor 22.
Each small rectangle represents an individual pixel (cell) of a CCD. The
TDI sensor 22 comprises in particular a sequence of cells 42, 44, 42, 44,
42, 44, 42 numbered 1 to N. In the example shown, N=7. In practice the
number of cells in the sequence is typically much larger. The sensor is
configured for shifting a charge from the cell numbered 1 (the top cell
42 in the Figure, in the first row 30) via the cells numbered 2 to N-1,
to the cell numbered N (the lowest cell 42 in the Figure, in the last row
32). Each cell 42, 44 is either sensitive or insensitive in the sense
that when the sensor 22 is evenly illuminated by light having a first
spectrum, the intensity of the light incident on any of the insensitive
cells 44 is at most 10% of the intensity of the light incident on any of
the sensitive cells 42. Although it is preferred that the intensity of
the light incident on any of the insensitive cells is as low as possible
(e.g. at most 10% or at most 20% of the intensity of the light incident
on any of the sensitive cells), the methods described in this application
could still work properly as long as the intensity of the light incident
on any of the insensitive cells is noticeably lower than the intensity of
the light incident on any of the sensitive cells if the TDI sensor is
evenly illuminated. Note that an even illumination of the TDI sensor is
assumed here merely for the purpose of characterizing the cells. In
practice, the TDI sensor is not evenly illuminated, but exposed to an
optical image of an object. In the example, the sequence of cells 42, 44,
42, 44, 42, 44, 42 represents an alternating series of sensitive cells 42
and insensitive cells 44. In the example, the sensitive cells 42 and the
insensitive cells 44 are all inherently light-sensitive in the sense that
they would accumulate a charge if they were exposed to light of a
suitable frequency (wavelength). They are rendered sensitive and
insensitive, respectively, by preventing incident light from reaching the
insensitive cells 44. To this end, the sensor 22 comprises opaque
elements 40 which are opaque for light having the first spectrum and
which mask the insensitive cells 44 but none of the sensitive cells 42.
Those rows 28 which are covered by one of the opaque elements 40 and
those which are not, are also referred to in this application as
unexposed rows and exposed rows, respectively, or as sensitive rows and
insensitive rows. It is noted that the sensor pixels (cells) have a
physical dimension in the scan direction (parallel to the x-axis) that is
half their extension in the perpendicular direction (parallel to the
y-axis), subsequent rows corresponding to a single image being separated
by twice the normal pixel distance. Alternatively, binning of the pixels
or subsampling of the image in the perpendicular direction can be done in
software. It is further noted that the last cell in the sequence could
alternatively be an insensitive cell. Thus a time interval for reading
out the last cell and a time interval for exposing the TDI sensor to
light could overlap without affecting the quality of the data that is
read out.

[0050] In a variation of the embodiment discussed above with reference to
FIG. 2, a striped color filter replaces the opaque elements 40. The
filter provides a mask that blocks only light of certain wavelengths.
With such a mask the TDI sensor may for instance be used as a time domain
multiplexing sensor for one wavelength range, while it can still work as
a `full` TDI sensor for other wavelengths.

[0051]FIG. 3 illustrates a method for acquiring signals on the TDI sensor
22 during a scan of the object 12 shown in FIG. 1, now employing instead
of the TDI sensor 22 shown there the modified TDI sensor shown in FIG. 2.
It is important to note that the object under study moves at a
substantially constant velocity during the scan. First, a first light
source (`source A`) is switched on (S1). A signal (`image A`) is acquired
on the sensor roughly for the time it takes the optical image of the
object to move over the height of one pixel (S2). Then source A is
switched off (S3), all charges on the sensor are moved to the next pixel
row (S4), and a second source (source B) is switched on (S5). Again, a
signal (`image B`) is acquired on the sensor roughly for the time it
takes the optical image of the object to move over one pixel (S6). Then
source B is switched off (S7), the charges are moved to the next row of
pixels (S8), and the whole process (steps S1 to S8) is repeated. Thus the
switching of the light sources is synchronized with the transfer of the
accumulated charge from each pixel row to the respective next row. An
output signal read from the last row of the sensor corresponds to rows of
pixels that are related to the different light sources in an alternating
manner. De-interlacing the output signal yields two-dimensional images,
each related to a different light source.

[0052]FIG. 4 illustrates a transfer of charges on the sensor 22 shown in
FIG. 2 from one pixel row 28 to the subsequent pixel row 28. The left
part of the Figure illustrates the situation just before the charges are
shifted. The right part shows the situation after the shift. Before the
shift, a part of image A has been built up on the exposed rows (shaded
rows 28 in the Figure) of the sensor, in the form of accumulated charges
while a part of image B was stored on the unexposed rows (white rows 28
in the Figure). Next, any charges stored on any of the exposed rows are
shifted downward to a subsequent unexposed row while any charges stored
on the unexposed rows are shifted downward to a subsequent exposed row.
Thus, after the transfer, part of image A is stored on the unexposed
rows, and part of image B is stored on the exposed rows. The values of
the charges in the last row 32 are read out and stored on a computer.
Light source B is then switched on to further build up image B on the
sensor. If the unexposed rows are not completely shielded from the
incident light so that they still receive a portion of the incident
light, the original images A and B can still be derived from the values
of the charges using image processing.

[0053] An extension of the embodiment illustrated with reference to FIGS.
2 to 4 involves more than two light sources. When M light sources are
used, only every Mth row is exposed to light, and a cycle of alternating
all light sources is matched with the scanning of M rows.

[0054]FIG. 5 illustrates a preferred embodiment in which an array of
lenses or microlenses is used rather than a simple absorbing or
reflecting mask. Shown is a side view of a TDI sensor 22 which is
illuminated by a plane wave of light 46. The light 46 is focused by an
array of cylindrical lenses 48 onto the rows of sensitive cells 42,
leaving no light to fall on the intermediate rows of insensitive cells
44. The cylindrical lenses 48 focus the light 46 only in the scan
direction (the x-direction). They thus generate focal lines (extending in
the y-direction) instead of customary focal spots. The cylindrical lenses
48 may be further combined with an intensity mask for preventing light
from reaching the insensitive cells 44 even more effectively.
Alternatively the array of lenses may be a two-dimensional array of
spherical focusing lenses.

[0055] The current invention may be used for any application involving
time domain multiplexing of a TDI sensor. Specifically, it may be applied
for fluorescence imaging with multiple fluorophores, for multiple color
brightfield imaging, and for combining fluorescence imaging with
brightfield imaging in a single scan.

[0056] While the invention has been illustrated and described in detail in
the drawings and in the foregoing description, the drawings and the
description are to be considered exemplary and not restrictive. The
invention is not limited to the disclosed embodiments. Equivalents,
combinations, and modifications not described above may also be realized
without departing from the scope of the invention.

[0057] The verb "to comprise" and its derivatives do not exclude the
presence of other steps or elements in the matter the "comprise" refers
to. The indefinite article "a" or "an" does not exclude a plurality of
the subjects the article refers to. It is also noted that a single unit
may provide the functions of several means mentioned in the claims. The
mere fact that certain features are recited in mutually different
dependent claims does not indicate that a combination of these features
cannot be used to advantage. Any reference signs in the claims should not
be construed as limiting the scope.

Patent applications by Erik Rene Kieft, Eindhoven NL

Patent applications by KONINKLIJKE PHILIPS ELECTRONICS N.V.

Patent applications in class Time delay and integration mode (TDI)

Patent applications in all subclasses Time delay and integration mode (TDI)